Presynchronization in Sheep Ensures Synchronization of Next Estrus and Improves Fertility

In this study, fertility was evaluated either in the first hormonally synchronized or in the subsequent natural estrus among 202 sheep during the breeding season. Intramuscular (im) PGF2α was administered 11 days apart in both the PG (n=50) and Pre-PG (n=50) groups, while im PGF2α was given at the removal of an intravaginal progesterone sponge (after 11 days) in the Sponge (n=51) and Pre-Sponge (n=51) groups. Estrus was monitored following the last hormonal application (day 0) in all groups and starting from day 16 in the Pre-PG and Pre-Sponge groups for 5 days. Ewes were mated during the first hormonally synchronized estrus (PG and Sponge groups) or in the next (natural) estrus (Pre-PG and Pre-Sponge groups). The estrus rate and litter size in the Pre-Sponge group were higher than those in the other groups (P<0.05). In the Pre-Sponge group, pregnancy and lambing rates were higher than in the PG and Sponge groups, and fecundity was higher than in the PG group (P<0.05). It was concluded that progesterone and PGF2α-based estrus synchronization may negatively affect fertility. Additionally, the next estrus is also synchronized after using progesterone and PGF2α-based synchronization protocols. Fertility loss caused by the application of exogenous hormones can be mitigated by mating at the next natural estrus. Furthermore, the next natural estrus can be utilized in situations where hormone use is inappropriate but synchronization is desired.